During recent decades, the growth of the plastics industry and an ever-increasing use of polymeric materials has coincided with an increasing awareness and concern for the safety hazards, especially fire hazards of materials. The result has been the development of a variety of fire retardant additives and fire retardant polymeric compositions. In past years, the major emphasis in the development of such fire retardant compositions has been in the achievement of low burning rates. More recently, however, there has been an increasing recognition of the hazards of smoke generation during fire and the advantages of char formation in inhibiting combustion. Furthermore, it is now more generally recognized that low burning rates do not necessarily imply or result in low smoke generation or beneficial char formation. As a result, the need is now recognized for the development of improved fire retardant polymeric systems having not only low burning rates, but low smoke generation and high char formation.
Among the developments in the field of fire retardant polymeric systems in recent years, the development of polymeric systems employing antimony trioxide as a fire retardant additive has been outstanding. Antimony trioxide has been found especially effective for use in systems based on halogen containing polymers. The effectiveness of antimony trioxide, as well as other antimony compounds as a fire retardant additive to halogen containing polymers is generally recognized and has been described as a synergistic effect between antimony and halogen. Despite its generally recognized effectiveness in such systems, the use of antimony trioxide, as well as other antimony compounds, has been found to result in certain disadvantages. For example, although the use of antimony compounds has been shown in many instances to advantageously decrease flammability and burning rate of polymer systems, it appears to provide little advantage in inhibiting formation of smoke and in some instances has been found to increase smoke formation. Furthermore, the use of antimony trioxide system may result in the diminution of other useful and desirable properties of polymer systems. Thus, for example, normally translucent polyester resins have been rendered opaque by the incorporation of sufficient quantities of antimony trioxide to render the resins fire retardant. In addition, in recent years, the rapidly rising cost of antimony compounds has been an economic disadvantage.
As a result of these disadvantages associated with the use of antimony compounds as fire retardant additives, considerable effort has been expended in a search for other fire retardant additives. However, the effectiveness of a particular fire retardant additive in a polymeric system is generally unpredictable and an additive useful in one polymeric system may be ineffective or even harmful when used in a different polymeric system. Even more unpredictable is the effect achieved when fire retardant additives are combined. Combinations of various fire retardant additives may result in a beneficial or detrimental formulation with a given polymeric system. Furthermore, combinations of fire retardant additives may benefit one aspect of fire retardance and be detrimental to another.
It is also known from Applicants' copending application Ser. No. 642,026, filed Dec. 18, 1975, which is the continuation-in-part of U.S. application Ser. No. 383,749, filed July 30, 1973, now abandoned, to employ iron compounds as fire retardant additives in halogen-containing unsaturated polyester resins.
In Applicants' U.S. Pat. No. 3,992,480 issued Nov. 16, 1976, filed June 6, 1975 as a continuation-in-part of application Ser. No. 383,747, filed July 30, 1973, now abandoned, it is disclosed that copper compounds can be advantageously employed as fire retardant additives in halogen containing unsaturated polyester resin.
In Applicants' aforementioned copending application Ser. No. 692,624 and the abandoned parent application thereof aforementioned Ser. No. 490,423 of which the present application is a continuation-in-part, it is disclosed that an additive mixture of iron or iron compounds with copper or copper compounds wherein the iron compound can be ferric molybdate or the copper compound can be copper molybdate imparts, synergistically, a low burning rate, low smoke generation and beneficial char formation to halogenated unsaturated polyester compositions.
Accordingly, it is an object of this invention to provide superior fire retardant unsaturated polyester resins that not only have low burning rates, but also exhibit low smoke generation when in contact with a flame.
It is also an object of the invention to provide superior fire retardant polyester resins that develop a beneficial, insulating layer of char in the presence of a flame which inhibits further combustion of the polymer.
It is still another object of the invention to render unsaturated polyester resins fire retardant without diminishing or deteriorating other useful properties of the polymer system.
It is a still further object of the invention to devise a fire retardant additive for unsaturated polyester resins which does not require the presence of antimony or an antimony compound.
These and other objects are accomplished by this invention which is described in detail hereinafter.